As shown in FIG. 1, a traditional base station 100 usually consists of controller boards 101, channel cards 102, clocking units 103 and radio cards 104, which all reside on a system backplane in the same chassis which includes a test bus 120 and a system bus 130. The system level test bus architecture is an extended Boundary Scan (BS) multi-drop bus architecture. It is made of the five BS TAP signals and contains a boundary scan master (BSM) 121 as a test bus master in the controller board 101. The controller board (card) 101 also includes a microprocessor 122. Each of the other boards contains an addressable scan port (ASP) device 115 as a test bus slave. This multi-drop test architecture supports embedded boundary scan, where the BS tests are embedded on the controller board 101 and executed by the microprocessor 122 as a part of system functions during field operation.
A Distributed Base Station (DBS) 200 is shown in FIG. 2, the Base Band Unit (BBU) 250 consists of controller boards 201, channel cards 202, clocking units 203 and fiber interface units (FIU) 206, as well as other types of cards not shown for reasons of clarity, on one local backplane which includes a test bus 220 and a system bus 230. A single-bit fiber 260 connects the BBU 250 with a radio frequency unit (RFU) 270 which consists of a radio card 204 and a fiber interface adapter (FIA) 207. The FIA 207 acts as a remote and distributed backplane for the radio card 204 in RFU 270. Furthermore, communication between BBU 250 and RFU 270 is accomplished by the communication of FIU 206 and FIA 207 via the long single-bit fiber cable 260. The FIU 206 and FIA 207 also include a serializer and de-serializer (SerDes) 209a, 209b which serialize and deserialize the data to and from, respectively, the single bit fiber cable 260. Over sampling and multiplexing design techniques must also be implemented due to the limited bandwidth between the pair SerDes 209a and 209b as shown in FIG. 2.
The DBS's unique distributed design enables mobile operators to deploy the RFUs 270, the components of a base station that send and receive radio signals, and power system separately from the BBUs 250, the components of a base station that process and send the radio signals to and from a mobile switching center (not shown). The RFUs 270 and BBUs 250 can be connected by a customer-provided single-mode fiber cable 260 at distances of 12 km or even higher. These single mode fiber cables can also include other types of tethers commonly used as backhaul, such metallic wire lines.
For example, in an urban environment, multiple BBUs 250 can be deployed at a company maintenance facility and connected to a mobile switching center via a T1 line, while the RFUs 270 are deployed miles away near major highways, train and bus stations and hospitals and are connected to the BBUs 250 via the single-mode fiber cable 260.
The DBS provides a compact, low cost unit for small or entry-level networks. It is designed for suburban build-out, hole filling, hot spots, in-building or any broad coverage, medium capacity network need. Flexible mounting options include poles, walls, roofs and various configurations in buildings.
A DBS is designed for increased capacity and coverage in the smallest footprint. Its compact construction reduces space requirements and real estate costs, which may significantly shorten the time to market through rapid site selection and zoning. In addition, the overall quality of network service improves via the ability of the DBS to provide coverage for a variety of environments. Furthermore, the DBS can use remote software control for remote maintenance, which results in fewer on-site visits and trimmed travel and labor costs.
The current disclosure presents a third-generation (3G) CDMA2000 base station that, because of its compact design and distributed architecture, offers the flexibility needed to meet a variety of deployment needs and coverage challenges for mobile operators.
However, the DBS poses great challenges for system testing and field update operation due to its distributed architecture since only a serial channel exists between the local and remote backplanes. More importantly, the serial channel is a functional channel, rather than a dedicated test channel such as the five BS TAP signals which connect the cards to the test bus 220.
One challenge is that the FIA 207 of the DBS is not only a distributed backplane for a radio card 204 but also the FIA 207 is a board in the distributed system. The problem arises how to effectively test the FIA 207 and the radio card 204 during system integration test and field operation.
The long fiber 260 causes significant propagation delay, which limits BS test clock (TCK) frequency. Usually a single-mode fiber incurs a 5 μs propagation delay per kilometer. For example, a 10 km long fiber (i.e., 20 km roundtrip) incurs a 100 μs roundtrip delay. Since BS test data output (TDO) changes only on the falling edge of TCK and BS test data input (TDI) is clocked on the rising edge of TCK, for a 50% duty cycle TCK there is only 0.5 cycles for a falling edge to travel to the FIA 207 and for data returning to FIU 206 (i.e., 0.5 cycle=100 μs). Hence, for this example, TCK must be slower than 5 kHz for proper operations. Additionally, due to the slow TCK frequency to accommodate long fiber delay, effectively updating the configuration PROMs of distributed units as previously discussed can be a challenge. Therefore, it becomes essential to slow down TCK for distributed system testing which has the disadvantage of increasing test and programming duration.
Another problem associated with the DBS is how to perform field update without on-site visits for the distributed RFUs 270. The design of the remote units must be robust enough so that a failure during remote field update does not cause the breakdown of the remote units and thus reduction of its reliability.
In order to obviate the deficiencies of the prior art and to address the above challenges, it is an object of the disclosure to present a novel distributed BS test bus architecture for transmitting BS TAP signals over a serial channel to facilitate distributed system testing and remote field update of a DBS, thereby enabling the system testing as if the distributed units are on a backplane within the same chassis.
These objects and other advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description of the preferred embodiments.